When this was already in print, I came across an article on ‘Porsons Gesetz’ by K. Witte in Hermes xlix. (1914), pp. 229–245, which led me to another article with the same title by J. Krái in Sitzungsberichte der königlböhmischen Gesellschaft der Wissenschaften, Klasse für Philosophic usw., Jahrgang 1909, ix. Král reckons the percentage of spondees in the fifth foot of the tragic trimeter at 43·4, and he has forestalled me in finding therein a partial explanation of Porson's Law. This suggestion is curtly dismissed by Witte, who sees in the predominance of iambs not a cause but a consequence of the Law.